Stormwater Management

Benefits and Considerations

"A 2007 U.S. EPA study found lower total costs for 11 of 12 green infrastructure projects when compared to equivalent grey infrastructure projects. The EPA study found the reliance on natural conveyance systems significantly reduced structural costs throughout the stormwater management chain. The opportunity to incorporate green infrastructure into other structures and landscaping also reduces the overall footprint of stormwater management infrastructure." -Jeffrey Odefey et al., Banking On Green: A Look at How Green Infrastructure Can Save Municipalities Money and Provide Economic Benefits Community-wide (American Rivers, Water Environment Federation, American Society of Landscape Architects, and ECONorthwest, 2012), 10.

Maintenance agreements are necessary to establish responsibility for the upkeep of the facility. Agreements may be secured through a specific city agency, neighborhood or business association, or be assumed by the adjacent business or property owner.6

Facility design must account for the physical constraints of the site, the presence of subsurface utilities, the local climate, and the feasibility of maintenance agreements. An experienced geotechnical engineer should verify partial or full infiltration conditions of the native soils. Native soil conditions, site slopes, native plantings, and location within the existing watershed should all be considered in the design process. Infiltration facilities should only be located in Class A or B soils.7

Application

Conventional stormwater management infrastructure has been engineered to move the largest volume of water from a site as quickly as possible, collecting surface runoff in subsurface structures.2 Sustainable stormwater management captures water closer to the source, reducing combined sewer overflows (CSOs), ponding, and roadway flooding. In the process, rain water issued as an asset to improve urban ecology, microclimates, air quality, and the aesthetic quality of the public realm.

Sustainable stormwater management aims to achieve the following goals:

Improve water quality
Vegetated strips and swales filter and reduce sediment and filter pollutants through settling, physical filtration in the soil matrix, biological breakdown by microbes, and nutrient uptake by plants.

Detain stormwater flows
Stormwater runoff is detained in facilities such as flow-through planters, pervious pavements, and bioswales. Detaining the flows mitigates the peak flow rates from the rain event, which in turn helps reduce erosion, loss of nutrients, scouring, and load-carrying capacity.3

Reduce stormwater volumes
Overall stormwater runoff volumes may be reduced by designing facilities that absorb and infiltrate rain water in place. Water-tolerant plant root systems maintain the porosity of the soil while taking up excess water in the stormwater facility.

Relieve burden on municipal waste systems
Sustainable stormwater systems reduce the amount of stress on a city’s wastewater treatment facilities, and may reduce long-term costs if applied at a citywide scale.4 Unlike traditional infrastructure, which does not add any additional value beyond its stormwater conveyance function, green infrastructure can be incorporated into neighborhood parks and landscaping.￼￼￼￼￼